A detergent insoluble, actin-containing matrix is associated with the inner surface of the plasma membrane of murine tumor and lymphoid cells. The matrix consists of seven major protein components. These proteins will be purified and characterized. Interactions of the individual components to form the matrix will be studied, as will interaction between the matrix and the membrane bilayer and cytoskeleton. Experiments will also be done to investigate dynamic aspects of the matrix interactions. These studies of this major component of the cytoplasmic face of the membrane should provide a better understanding of processes such as transmembrane signalling and cell surface protein redistribution, processes crucial to the normal functioning of lymphocytes in the immune system.